To reduce heat and conserve energy in building windows, vehicle windows, cold storage or refrigeration showcase windows, and the like, there is demand for these windows to be endowed with the property of reflecting or absorbing heat rays (infrared rays), and one method of doing so is to affix transparent heat ray shielding adhesive sheets to the windows.
One method of creating a conventional highly transparent heat ray shielding adhesive sheet is to form a dielectric multilayer thin film, a metal film, or a thin transparent electroconductive film as a heat ray shielding layer on a transparent sheet using sputtering, vapor deposition, or the like, and to also apply a coating of an adhesive.
Patent Reference 1 proposes a transparent film with a heat ray shielding film, in which a hard coat layer containing antimony-containing tin oxide microparticles or tin-doped indium oxide microparticles are formed on one surface of a transparent film substrate, a laminated-layer structured film containing an adhesive layer and a peeling layer sequentially laminated is formed on the other surface, and the hard coat layer also serves as a heat ray shielding layer. However, a problem with these methods is that two or more different film-forming steps are needed when creating a heat ray shielding adhesive sheet, and the demand for a simpler method for manufacturing a heat ray shielding transparent sheet has led to endowing the adhesive rather than the sheet with the heat ray shielding property.
Patent Reference 2, for example, discloses the idea of adding a substance having an optical selective absorption characteristic to an adhesive to manufacture an adhesive film having an optical selective absorption characteristic at low cost, but discloses nothing whatsoever concerning the specific manufacturing method, the blending of the adhesive, or the like.
Patent Reference 3 discloses a coating agent which uses hydrophobic antimony-containing tin oxide and a binder resin and which is transparent for visible light but which shields heat rays, and Patent Reference 4 discloses an adhesive sheet which contains heat-ray-shielding microparticles in a hard coat layer or an adhesive layer, and which is transparent for visible light but which shields only heat rays.
However, this adhesive sheet has a three-layer structure containing a heat ray shielding layer, an adhesive layer, and a hard coat layer, and a problem with this sheet is that the object of simplifying the manufacturing steps cannot be achieved.
Patent Reference 5 discloses that the endowing of transparency and heat ray shielding is simplified by dispersing heat-ray-shielding microparticles in an adhesive, and also discloses a heat ray shielding adhesive, a manufacturing method thereof, and a heat ray shielding transparent sheet. However, this heat ray shielding transparent sheet has insufficient transparency in the visible light range and haze, and there is demand for further improvement in transparency in the visible light range, haze, and heat ray shielding.